Genes can be transferred to and expressed in cells that ordinarily do not harbor them. In preliminary studies we transferred the rat growth hormone (rGH gene) to mouse L cells by cotransformation of thymidine kinase defective (TK-) cells with the herpes simplex virus (HSV) TK cells will not grow. In the transformed cells, rGH gene transcripts were present and their levels were increased by the glucocorticoid dexamethasone. In the proposed studies, we hope to exploit this system to understand better the structure(s) on DNA important for glucocorticoid control. The first set of experiments focuses on transformed lines already obtained to determine: (1) the kinetics and specificity of the response; (2) if the effect on rGH mRNA is mediaed by glucocorticoid receptors; (3) the fraction of rGH gene-containing cell lines in which rGH gene expression is regulated by glucocorticoids; (4) the processing of the transcripts and the hormonal effect on this; (5) the 5'-terminus of the transcripts; (6) the rGH gene structure in the transformed cells; (7) whether rGH mRNA levels can be regulated positively or negatively by glucocorticoids; (8) and whether the hormonal effect on mRNA levels is due to influences on transcription or on RNA stability. The second group of experiments focuses on DNA fragments deleted in portions of the rGH gene to determine those structures important for its expression and its capability to be glucocorticoid regulated. In the third series of experiments, hybrid genes will be constructed containing the rGH gene fused to the HSV TK gene (and possibly othe genes) to see if the capability for glucocorticoid control can be conferred on the TK gene. In the fourth series of experiments, the set of GH-related genes will studied following their transfer to L cells. These genes vary in the response of their expression to glucocorticoids. Thus, the human(h) GH expression may be increased whereas rat prolactin (rPrl) and probably hPrl mRNA levels are ordinarily depressed by the setroid and placental lactogen (PL) mRNA is not known to be affected. Since these genes share substantial sequence homology, it should be possible to delineate structure(s) important not only for positive but also for negative regulatory effectsof flucocorticoids and to derive consensus sequences that may be involved directly or indirectly in glucocorticoid action.